One such continuum scheme is to regard the field as an estimate of the density
of points (say in units of galaxies per cubic parsec), smoothed on scales at
least as large as the typical distance between points, and very much larger
than the sizes of the galaxies, which are after all treated as points
of zero size. Excellent overviews of the mathematical aspects of multivariate
densities and their estimation from point data are to be found
in [1]}, [2]}. Discussions of this concept
in relation to the large-scale
structure of the Universe are found in [3]}, [4]}, [5]}.
